On 12/06/2012 12:37 AM, Oleg Nesterov wrote:
> I'll try to read this series later,
>
> one minor and almost offtopic nit.
>
> On 12/06, Srivatsa S. Bhat wrote:
>>
>> static int __ref take_cpu_down(void *_param)
>> {
>> struct take_cpu_down_param *param = _param;
>> + unsigned long flags;
>> int err;
>>
>> + /*
>> + * __cpu_disable() is the step where the CPU is removed from the
>> + * cpu_online_mask. Protect it with the light-lock held for write.
>> + */
>> + write_lock_irqsave(&light_hotplug_rwlock, flags);
>> +
>> /* Ensure this CPU doesn't handle any more interrupts. */
>> err = __cpu_disable();
>> - if (err < 0)
>> + if (err < 0) {
>> + write_unlock_irqrestore(&light_hotplug_rwlock, flags);
>> return err;
>> + }
>> +
>> + /*
>> + * We have successfully removed the CPU from the cpu_online_mask.
>> + * So release the light-lock, so that the light-weight atomic readers
>> + * (who care only about the cpu_online_mask updates, and not really
>> + * about the actual cpu-take-down operation) can continue.
>> + *
>> + * But don't enable interrupts yet, because we still have work left to
>> + * do, to actually bring the CPU down.
>> + */
>> + write_unlock(&light_hotplug_rwlock);
>>
>> cpu_notify(CPU_DYING | param->mod, param->hcpu);
>> +
>> + local_irq_restore(flags);
>> return 0;
>
> This is subjective, but imho _irqsave and the fat comment look confusing.
>
> Currently take_cpu_down() is always called with irqs disabled, so you
> do not need to play with interrupts.
>
> 10/10 does s/__stop_machine/stop_cpus/ and that patch could simply add
> local_irq_disable/enable into take_cpu_down().
>
Hmm, we could certainly do that, but somehow I felt it would be easier to
read if we tinker and fix up the take_cpu_down() logic at one place, as a
whole, instead of breaking up into pieces in different patches. And that
also makes the last patch look really cute: it just replaces stop_machine()
with stop_cpus(), as the changelog intended.
I'll see if doing like what you suggested improves the readability, and
if yes, I'll change it. Thank you!
Regards,
Srivatsa S. Bhat
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